Encrypted email service provider Lavabit is shutting down, but a gag order prevents the company from detailing exactly what triggered that business decision.

Ladar Levison, the owner and operator of Texas-based Lavabit, said in a statement that his hand was forced after six weeks of legal wrangling and two attempts by him to squash the gag order, both of which were rejected by a judge. As a result, he's not at liberty to publicly reveal exactly what's going on.

"I have been forced to make a difficult decision: to become complicit in crimes against the American people or walk away from nearly 10 years of hard work by shutting down Lavabit," he said. "After significant soul searching, I have decided to suspend operations. I wish that I could legally share with you the events that led to my decision. I cannot."

Lavabit had promised that it would be an "e-mail service that never sacrifices privacy for profits" and "only release private information if legally compelled by the courts in accordance with the U.S. Constitution." The service backed up those claims by storing only encrypted versions of emails on its servers, which could only then be decrypted using a user's passphrase, which the service didn't store.

Lavabit's closure led startup company Silent Circle to announce Thursday that it would shutter Silent Mail, which is its encrypted email service. "We see the writing [on] the wall, and we have decided that it is best for us to shut down Silent Mail now. We have not received subpoenas, warrants, security letters, or anything else by any government, and this is why we are acting now," said Silent Circle CTO Jon Callas in a blog post.

Privacy rights advocates slammed the secret legal maneuvers by the government that lead to the closures. "We need more transparency so the public can know and understand what led to a ten-year-old business closing its doors and a new start-up abandoning a business opportunity," said Kurt Opsahl, a senior staff attorney at the Electronic Frontier Foundation (EFF), in a blog post.

In response to the two services being shuttered, the team behind the free, open source GPG Suite offered their software as an alternative. "We're sorry to hear that lavabit and silent mail shutdown [sic]. OS X users wanting to protect your mails, have a look at https://gpgtools.org," they tweeted.

But in his blog post, Silent Circle's Callas suggested that technologically speaking, any type of crypto email may offer less security than it seems. "Email that uses standard Internet protocols cannot have the same security guarantees that real-time communications has. There are far too many leaks of information and metadata intrinsically in the email protocols themselves," he said. "Email as we know it with SMTP, POP3, and IMAP cannot be secure."

Furthermore, leaked National Security Agency (NSA) operating guidelines suggest that simply using encryption tools draws extra scrutiny from the agency's analysts. Encrypted communications, when intercepted, are also exempt from protections afforded to Americans' regular communications. While ordinary communications can legally only be retained by the NSA for six months, unless they contain evidence of a crime, encrypted communications may be retained indefinitely.

Lavabit's Levison sounded a further ominous note for anyone storing any type of sensitive data with a third party. "This experience has taught me one very important lesson: without congressional action or a strong judicial precedent, I would _strongly_ recommend against anyone trusting their private data to a company with physical ties to the United States," he said.

What lead to the U.S. government -- or intelligence services -- taking an apparent interest in Lavabit? The most likely answer is that NSA whistleblower Edward Snowden used the service. That was revealed last month when Tanya Lokshina, a senior Russia researcher for Human Rights Watch in Moscow, published a copy of an emailed invitation asking her to attend a meeting at the local Sheremetyevo airport to discuss Snowden's bid for asylum, sent from "edsnowden@lavabit.com." Snowden also used Hushmail and PGP encryption.

The closure of two well-regarded crypto email services is the latest chapter in the ongoing saga kicked off by Snowden's leaking of documents -- not all of which have been published -- that detail secret NSA programs, including the agency's wide-ranging digital dragnet that captures and stores the everyday communications of millions of Americans. That state of massive surveillance is aided by a secretive Foreign Intelligence Surveillance Court that in recent years has apparently compelled technology providers -- including Facebook, Google and Microsoft -- to provide the NSA with easy access to their users' communications.